A phenomenon of emitting light in a mechanical method, that is, light generated by applying a strength to a material has been known as mechanoluminescence (a superordinate concept including triboluminescence, fractoluminescence, deformation-luminescence, etc.) for a long time, but a principle of emitting the light is uncertain even until now and also has been treated as only an academic interest.
For example, X-ray emission due to a separation phenomenon of scotch tape in a vacuum (Camara et al. Nature 2008) and ultraviolet (UV) ray emission due to an ultrasonic wave (Eddingsaas et al. Nature 2006), etc. caused a great response academically, but industrial applicability is very low due to a fundamental problem that the light is generated by friction or destruction.
In order to solve the problem related to the industrial applicability, Xu group of the Japanese National Institute of Advanced Industrial Science and Technology (AIST) has tried to apply a non-destructive mechanoluminescent phenomenon, which is deformation luminescence generating the light by elastic or plastic deformation in some materials, to a stress sensor instead of triboluminescence and fractoluminescence generated due to a phenomenon such as friction and destruction.
However, a UV cured polymer is used as a stress transmission material transmitting a mechanical strength to a luminescent material, which is a parent material of emitting light, and thus a lifetime is extremely limited since it is difficult to apply repeated stresses. Further, studies related to the mechanoluminescence are limited to the luminescent material itself until now, and there are no studies related to the stress transmission material transmitting the stress.
Further, in order to apply the mechanoluminescent phenomenon to various industries, brightness, a lifetime, and a color control are very important factors, but many studies have not been performed due to a limitation of the material itself until now. Particularly, technological developments related to the color control do not exist due to the brightness of the light emitted from the material and the limitation of the lifetime (or reproducibility).